ehaust question D15 B16

Right now I have the D15 motor and i'm going to use it for a while because it only has 33K on the motor. I am saving up for a B16 swap. My question is about what size exhaust I should use. I already have the muffler and i'm going to get a header for the b16 but I don't want to waste any money on the D motor. So what size exhause should I go with? I want to go atleast 2 1/4" but with the B series do i want to go any larger and will it make a difference? Thanks for the advice

I say 2 1/4" for n/a :)

okay thanks for the advice.